Effect of Accelerator on Compressive Strength Development of Class F Fly Ash Concrete

Abstract

Effect of accelerator on compressive strength development of concrete made by utilizing a mixture of 90% type I Portland cement and 10% class F fly ash a hydraulic binder has been studied. Natural sand was used as fine aggregate and crushed stone as coarse aggregate. The grain distribution of natural sand and crushed stone were designed according to Indonesian Standard SNI 03-2834-2000 to meet the gradation zone 2 for fine aggregate and the granules with a maximum diameter of 20 mm for coarse aggregate. The mix proportion of concrete, by weight, was 1.0 binder: 2.0 fine aggregate: 3.0 coarse aggregate and water-binder ratio was 0.5. The accelerator added to the concrete mixture was 2.5%, 5%, 7.5% and 10% by weight of mixing water. The control concrete was made without using the accelerator. Compressive strength test realized on cube specimens sizing of 150 mm x 150 mm x 150 mm at the age of 1, 3, 7, 28, 90 days. The test results showed that the addition of accelerator in the concrete mixture accelerates the development of concrete compressive strength, especially at the age of 1 day, compared to control concrete. At this age, with the addition of 2.5%, 5%, 7.5% and 10% accelerator, the compressive strength of concrete increases by respectively 31.8%, 31.1%, 27.1% and 24.1%. It was also noted that the addition of accelerator on the concrete mixture produces higher compressive strength at the age of 90 days compared to control concrete. It is finally found that the optimal use of accelerator to produce the greatest acceleration for the development of compressive strength in the early age and the highest compressive strength on the long period is 2.5%. On that optimal use, the development of the compressive strength of concrete at 1 day is accelerated about 31.8% and the compressive strength of concrete at 90 days is about 12.5% higher compared to control concrete.